FIG. 1 (Prior Art) is a diagram of a T-type three-level Neutral-Point-Clamped (NPC) phase leg module 1. Such a module sees use in applications including solar inverter, motor drive and UPS applications. The module is referred to as a “three-level” module because the module couples an output node AC to a selected one of three DC voltage power terminals. As compared to conventional two-level topologies, a T-type three-level topology may provide advantages in a given application. For example, a T-type three-level topology may allow transistors within the module to have lower breakdown voltages than they would otherwise be required to have were a two-level topology used, with the added advantages of better conduction and switching performance resulting in lower losses. Also a T-type three-level topology may allow a motor to be driven while emitting a reduced amount of electromagnetic energy. When the module is performing its switching function, the amount of emitted electromagnetic radiation generally must be below an allowable limit. The three-level topology may reduce the cost of filtering necessary to reduce emitted electromagnetic energy so that it will be below the allowable limit.
The constituent transistors, diodes and other components of a T-type three-level NPC phase leg circuit can be provided in different types of packages. In a low power application, a T-type three-level NPC phase leg circuit may be realized in one power module package. In a higher power application, a T-type three-level NPC phase leg circuit may have to be realized in multiple module packages due to heat dissipation limitations of a single module package and due to a lack of mounting area because of the required die size for the high current.
FIG. 1 is a top-down diagram of a T-type three-level NPC phase leg circuit that is realized in a single power module package. The module 1 includes an injected molded plastic housing 2 that is formed around a metal base plate. Four power terminals 3-6 extends outward from the housing 2 as illustrated. The power terminals are standard screw terminals for making electrical connections of bus bars or wires. The bottom side of the module can be attached to a heatsink or other body via screws (not shown). The screws are made to extend through corresponding mounting holes 7-10 in mounting flaps of the housing so that the screw heads hold the bottom side of the module (the metal base plate) down onto the heatsink. In addition to the four power terminals, there are smaller upwardly extending signaling/control terminals. The smaller upwardly extending signaling/control terminals are disposed in two rows. These upwardly extending signaling/control terminals extend upward out of the upper surface of the plastic housing. One of these signaling/control terminals of the upper row is identified with reference numeral 11.
FIG. 2 (Prior Art) is a circuit diagram of the T-type three-level NPC phase leg circuit of module 1 of FIG. 1. The circuit includes four Insulated Gate Bipolar Transistors (IGBT) 12-15 and four fast recovery diodes 16-19. IGBTs 14, 15 and diodes 18 and 19 are sometimes referred to as the DC-link. A positive DC voltage is generally supplied onto the P power terminal 3. A negative DC voltage is generally supplied onto the N power terminal 4. Ground potential (zero volts) is generally supplied onto the 0 neutral power terminal 6. In operation, current can be conducted from the P power terminal 3 to the output AC output terminal 5 by making IGBT 12 conductive. Current can be drawn from the AC output terminal to the N power terminal 4 by making IGBT 13 conductive. The AC output terminal 5 can be coupled to ground potential by making the DC-link conductive. The average current supplied out of the module via the AC output terminal to a load, or received onto the module via the AC output terminal from the load, is controlled by pulse-width modulating the IGBT gate signals of the various IGBTs of the module.
There are many considerations involved in the design of three-level NPC phase leg circuits, including the reduction of stray inductances. For additional background information, see, for example: 1) A New Neutral-Point-Clamps PWM Inverter, by Akira Nabae et al., IEEE Transactions on Industry Applications, Vol. IA-17, No. 5, pages 518-523 (1981); 2) Comparison of the Chip Area Usage of 2-Level and 3-Level Voltage Source Converter Technologies, by Mario Schweizer et al., Proceedings of the 36th Annual IEEE Industrial Electronics Society Conference, pages 391-396 (2010); 3) IGBT Power Modules Utilizing New 650VV IGBT and Emitter-Controlled Diode Chips For Three Level Converter, by Zhang Xi et al., Proceedings of the PCIM Europe 2009 Conference, pages 117-122 (2009); 4) Advantages of NPC Inverter Topologies With Power Modules, by Michael Frisch et al., www.Vincotech.com, 3 pages (2009); and 5) Power Module With Additional Low Inductive Current Path, Michael Frisch et al., 2010 Power Electronics Europe, Issue 7, pages 22-27 (2010).